Dual dynamic bonds enable biocompatible and tough hydrogels with fast self-recoverable, self-healable and injectable properties

High-strength hydrogels with injectable ability provide possibility of in vivo delivery in a minimally invasive way, but conventional tough hydrogels with excellent mechanical properties are difficult to be injected duo to their robust network structures. Here, smart hydrogels were synthesized by a simple one-pot strategy through the synergistic combination of acylhydrazone bonds (the first cross-linker) and H-bond cooperativity (the second cross-linker) two dynamic cross-linkers. The hydrogels exhibited excellent mechanical strength (369.7 KPa tensile stress, 73.2 MPa compressive stress, 5724 J m(-2) tearing energy), fast self-recovery (ca. 91% toughness recovery within 1.0 min), fatigue resistance and self-healing property. Notably, injection way was allowed to obtain hydrogels with any desired shape based on their remarkable switchable strength upon the alteration of pH, and the reformed hydrogels still exhibited high mechanical strength. In addition, a good cytocompatibility for the hydrogels was observed. Thus, this investigation may provide a promising strategy for the fabrication of biocompatible and injectable hydrogels with comprehensive mechanical properties by taking advantage of the synergistic effects of dynamic covalent bonds (DCBs) and physical interaction cross-linkers, and the hydrogels find potential applications in biomedical field, such as stressful working tissues.